IP Multimedia Subsystem (IMS) is a communication architecture that has been developed by the Third Generation Partnership Project (3GPP) as an open standard for handling various multimedia applications and sessions in the IP (Internet Protocol) packet domain (for details regarding IMS, please refer to http://www.3gpp.org/ftp/Specs/html-info/23228.htm). IMS manages the signaling between different communication devices, including mobile phones, personal computers (PC), personal digital assistants (PDA) and the like, by creating IMS sessions, which are authenticated and authorized. In this way the IMS system sets up a session through a number of different nodes between the initiator and the receiver over cellular network(s) and the Internet. In addition, IMS provides communication services such as QoS (Quality of Service), billing, and integration of different services.
Multimedia distribution such as IPTV (Internet Protocol Television) is one of the major IMS applications. In a digital media distribution system, digital rights management (DRM) technologies for controlling use of digital media are important for maintaining an orderly digital media distribution market. Particularly for “pay-per-view” services, it is desirable to be able to ensure that the digital media is neither re-usable nor redistributable after the expiry of a session. However, IMS itself does not provide such a DRM mechanism.
United States Patent Application Publication No. US 2005/0005146 A1 describes a system for automatically authenticating media stream recipients. In the authentication system, a media stream includes a self-installing and self-executing media player and media content. The media player communicates with an authentication service to acquire an authentication token. The authentication token is used by the media player in order to obtain access to and play media content on behalf of an authorized recipient. Authentication of media recipients effectively prohibits unauthorized clients from illegitimately receiving media objects. However, US 2005/0005146 A1 does not handle the problem of prohibiting authorized recipients from replaying or redistributing media objects after expiry of a given session.
The Open Mobile Alliance (OMA) DRM specification Candidate Version 2.0 (which can be downloaded from http://member.openmobilealliance.org/ftp/Public documents/DRM/), Appendix C, describes a general concept of applying OMA DRM to streaming services. Moreover, 3GPP Technical Specification titled Transparent End-to-End Packet-switched Streaming Service (PSS), Protocols and Codecs, Release 7 (which can be downloaded from http://www.3gpp.org/ftp/Specs/archive/26_series/26.234/) describes the end-to-end packet switched service standard from 3GPP, and Annex K describes a mechanism to encrypt the content of a media stream (RTP payload and so on). However, these documents do not describe any specific constructions regarding copyright protection for distributed media objects after session expiry and, in particular, do not describe any specific constructions regarding copyright protection for streaming media objects.